The rapid expansion of communication services are facilitating more and more users to access and use broadband services that are emerging one after another. In the meanwhile, the proportion of Internet Protocol (IP) services that are growing explosively is also increasing in communication networks, which evidently changes traffic characteristics of the communication networks, and dominant traditional voice services having relatively steady traffic in communication services are gradually replaced by data packet services with frequent traffic bursts, thereby greatly increasing network demands for flexible large capacity bandwidth allocation. In view of a development trend of service interfaces and optical transceiver technologies, a future optical network should be able to dynamically and flexibly provide different transmission rates and sub-wavelength level all optical switching capabilities of different bandwidth granularities.
A novel Optical Burst Transport ring-Network (OBTN), which is able to not only well adapt to bursts of data services, but also effectively reduce strict requirements of an all optical network on optical devices, is fully feasible with a flexible networking capability. FIG. 1 shows a network topology of an OBTN, in which a data channel consists of several wavelengths (in which the wavelengths are λ0, λ1, . . . λN, where N is a positive integer) used for carrying optical burst data, a control channel applies an independent wavelength λc to carry control information including bandwidth allocation, timeslot synchronization and so on, a data frame and a control frame are processed separately at respective network nodes, and a network node receives and sends a service correspondingly for the data frame according to control information. Optionally, each OBTN network node applies a fixed wavelength transmitter and a tunable wavelength receiver.
The OBTN uses a burst as the smallest network switching unit. Each burst is composed of two parts, a Burst Control Packet (BCP) and a Burst Data Packet (BDP), both of which are transmitted separately on physical channels. After acquiring control information, a network node can implement all optical switching or transparent transmission of the data packet without waiting for acknowledgement. Such a method of separating a control channel and a data channel not only largely simplifies switching of burst data, but also avoids a defect that a current optical buffer technology is immature, and reduces the complexity in implementing a network node.
The key to implement the OBTN based on medium sharing is to provide a highly efficient Medium Access Control (MAC) technology, i.e. a dynamic resource scheduling mechanism. At present, the OBTN generally applies token access or a random access method based on collision detection, both of which are, technically, distributed control management. However, a distributed MAC technology is easy to cause contention collision of burst data packets, thus resulting in waste of bandwidth resources of the optical burst ring network. Besides, it is also necessary to add a proper control protocol to the distributed MAC technology so as to provide fairness guarantee, and a processing time delay of a network node for control information is added preferably.
In fact, a centralized MAC technology based on timeslot division can better improve the network performance. A node in the ring network is selected as a master node, and other nodes are slave nodes. The master node is responsible for major functions of a control plane, mainly including: gathering bandwidth requests of nodes of the whole network, allocating bandwidths according to related resources, updating and delivering a bandwidth map and so on; and a slave node correspondingly receives and sends the bandwidth map delivered by the master node. In a centralized control solution, all bandwidth scheduling strategies are controlled by the master node, which can consider network resources comprehensively, improve the utilization ratio of bandwidths to the largest extent, provide fairness guarantee and reduce collision and contention.
Due to ring network characteristics of the OBTN, dynamic bandwidth resource scheduling at the master node needs to consider the influence of a cross master node service, wherein the cross master node service refers to a data packet that needs to pass the master node before being received on a source node and transmitted to a corresponding destination node to be transmitted, while a non-cross master node service refers to a data packet that does not need to pass the master node after being received on a source node and before being transmitted to a corresponding destination node to be transmitted. Taking FIG. 2 as an example, a slave node Node5 receives, at a certain moment T1 according to a current bandwidth map, a data service transmitted to a destination node Node3, and after a period of time δ, a control frame containing a bandwidth map arrives at a master node Node1 again. At the moment, the master node allocates bandwidths according to new bandwidth requests. Thus, after the control frame containing the latest bandwidth map is delivered from Node1, Node2 may also receive, at the timeslot m according to the latest bandwidth map, the data service sent to the destination node Node3. However, a data service sent by Node5 to Node3 at the timeslot m of a data frame has not yet been transmitted at the moment, and the two will have collision inevitably. Even if Node2 does not receive the data service sent to Node3 at the timeslot m, Node3 will receive the service according to the new bandwidth map when the control frame and the data frame arrive at Node3, and it is also possible that a data service sent by Node5 at the timeslot T1 will not be acquired.